1. Field of the Invention
The present invention relates to an optical scanning observation apparatus.
This application is based on Japanese Patent Application No. 2007-063822, the content of which is incorporated herein by reference.
2. Description of Related Art
Known laser-scanning microscopes in the related art transmit excitation light and detection light, for in vivo observation of an animal or the like, using a single optical fiber (for example, see Japanese Unexamined Patent Application, Publication No. 2005-300278 and Japanese Unexamined Patent Application, Publication No. 2006-79000). These laser-scanning microscopes employ a structure in which a collimator optical system between the fiber and a scanning mirror (an internal focusing mechanism) is driven to change the working distance, without changing the relative distance between an objective lens and a sample. With these laser-scanning microscopes, the tip of the objective lens can be brought into close contact with the sample to reduce the effects of breathing and pulsating of the animal. They are therefore optical scanning microscope systems designed for observation of animals.
On the other hand, configurations have also been disclosed in which the light path for excitation (excitation fiber) and the light path for detection (detection fiber) are separated to improve the signal-to-noise (SN) ratio (for example, see Japanese Unexamined Patent Application, Publication No. 2005-202338).
In addition, some known microscopes use an internal focusing mechanism (for example, see Japanese Unexamined Patent Application, Publication No. 2004-317676). Laser light is focused by a positive lens, is returned to a collimated beam with another positive lens, and is radiated onto a sample via a deflection mirror, a beam expander, and an objective lens. Fluorescence from the sample travels along the reverse light path, is split off from the laser light by a dichroic mirror, and after passing through a focusing lens and a pinhole, is detected by a detector. The working distance (WD) is changed by moving the positive lens. In this case, the optical system for changing the focus position is of the Keppler type. By combining Japanese Unexamined Patent Applications, Publication Nos. 2005-202338 and 2004-317676, it is possible to realize a microscope having an internal focusing mechanism with a high SN ratio.
However, with the configuration in Japanese Unexamined Patent Application, Publication No. 2004-317676, it is necessary to temporarily focus the light between the two lenses. Theoretically, it is possible to reduce the focal lengths of the positive lenses to reduce the overall length, but the change in position of the lenses then becomes small in relation to the change in focal position at the sample as the focal lengths are reduced. As a result, positional control becomes more difficult. Furthermore, because the numerical aperture (NA) between the two groups of positive lenses becomes large, aberration correction becomes difficult.
For these reasons, a long focal length is unavoidable. As a result, when combining the technologies in Japanese Unexamined Patent Applications, Publication Nos. 2005-202338 and 2004-317676, the overall length of the focusing optical system unavoidably increases, resulting in the drawback that the observation apparatus (microscope) increases in size, making it unsuitable for in vivo observation of animals.